Electrolytic Deposition Treatment Apparatus and Method

ABSTRACT

The present invention provides an electrolytic deposition treatment apparatus and method which can reduce metal ion concentration of waste water to be treated by electrolytic deposition to the degree to which treated water can be discharged to the outside, and which can treat waste water, even if the quantity of waste water produced in a semiconductor device fabrication apparatus is large.  
     The electrolytic deposition treatment apparatus comprises a cathode( 3 ) for depositing metal ions in water to be treated as metal, a cation exchange membrane( 4 ) disposed so as to face the cathode( 3 ), and an anode( 6 ) disposed so as to face the cation exchange membrane( 4 ) through a cation exchanger( 5 ). The water to be treated is supplied to a space between the cathode( 3 ) and the cation exchange membrane( 4 ).

TECHNICAL FIELD

The present invention relates to an electrolytic deposition treatment apparatus and method for removing metals efficiently and highly from various kinds of liquids and recovering the metals continuously in the form of granules or powder.

BACKGROUND ART

Various kinds of waste water, such as those produced in plating processes, semiconductor device fabrication processes, printed circuit board fabrication processes, or mines, contain valuable noble metal ions in relatively small quantities and heavy metal ions which is the subject of restrictions on its release to the surroundings in view of the environmental issue.

In treatment of such waste water containing the noble metal and the heavy metal, it has been required to sufficiently recover the noble metal contained in the waste water, remove the heavy metal to such a degree that waste water becomes harmless enough to be released to the surroundings, and recover the removed heavy metal as needed.

For example, in fabrication processes for semiconductor devices such as semiconductor integrated circuits, demands for semiconductor devices having finer interconnections or elements have further increased in recent years to thereby cause a problem of signal delay due to-interconnection resistance. In order to solve this problem, aluminum or tungsten is replaced with copper for interconnections.

Specifically, as semiconductor chips such as central processing units (CPU) or dynamic random access memories (DRAM) have become more highly integrated, materials for interconnections in semiconductor chips, particularly for interconnections having a minimum width of 0.13 μm or smaller, have changed from conventional aluminum into copper which has an electrical resistance lower than aluminum.

It is difficult to etch a copper layer in a semiconductor chip to form a pattern in the semiconductor chip. Therefore, when copper is used for interconnections in semiconductor chips, a semiconductor substrate is plated with copper by damascene process to deposit a copper layer on the semiconductor substrate, and then a surface of the copper layer is polished by chemical mechanical polishing (CMP) or electrochemical polishing (ECP) to form interconnections on the semiconductor substrate.

FIGS. 6A thorough 6E show an example of a process for forming an interconnection on a semiconductor substrate. As shown in FIG. 6A, first, a conductive layer 202 is formed on a semiconductor substrate 201 on which semiconductor devices have been formed, and an insulating film 203 of SiO₂ is deposited on the conductive layer 202. A contact hole 204 and an interconnection groove 205 are formed in the insulating film 203 by lithography etching technology. Then, as shown in FIG. 6B, a barrier layer 206 is formed on the insulating film 203. The barrier layer is made of metal such as Ta, TaN, TiN, WN, SiTiN, CoWP, or CoWB, or metallic compound thereof. In a case of forming a copper layer by electrolytic plating, as shown in FIG. 6C, a copper seed layer 207, which is used as a feeding layer in electrolytic plating, is further formed on the barrier layer 206 by sputtering or the like. In a case of forming a copper layer by electroless plating, a catalyst layer 207 is formed on the barrier layer 206 by pretreatment instead of the copper seed layer.

Subsequently, as shown in FIG. 6D, electrolytic copper plating or electroless copper plating is applied onto a surface of the copper seed layer 207 or the catalyst layer 207 to fill the contact hole 204 and the interconnection groove 205 with copper and to deposit a copper layer 208 on the insulating film 203. Thereafter, the copper layer 208 on the insulating film 203 is removed by chemical mechanical polishing (CMP) or electrochemical polishing (ECP) so that a surface of the copper layer 208 filled in the contact hole 204 and the interconnection groove 205 is substantially flushed with a surface of the insulating film 203. Thus, as shown in FIG. 6E, an interconnection comprising the copper seed layer or the catalyst layer 207, and the copper layer 208 is formed in the insulating film 203.

Under such circumstances, waste water containing a large number of copper ions is produced in an electrolytic copper plating process and an electroless copper plating process in a semiconductor device fabrication process, and a chemical mechanical polishing (CMP) process and an electrochemical polishing (ECP) process for microchips having integrated circuits. With respect to an allowable limit of copper ions contained in waste water, a maximum concentration of copper ions is restricted to 3.0 mg/l (liter) or lower in Japan. In the United States, a concentration of copper ions is more strictly limited than in Japan. For example, a maximum concentration of copper ions is restricted to 2.7 mg/l or lower, an average concentration of copper ions per day is restricted to 1.0 mg/l or lower, and an average concentration of copper ions per year is restricted to 0.4 mg/l or lower. Therefore, there has been strongly required to provide technology capable of efficiently removing copper from waste water.

In a present type of semiconductor device fabrication plant, a single CMP apparatus produces waste water having a maximum flow rate of about 0.5 m³/h and having a maximum copper concentration of about 100 mg/l in waste water. A single copper plating apparatus produces waste water having a maximum flow rate of about 0.2 m³/h and having a maximum copper concentration of about 100 mg/l in waster water. In average fabrication plants for semiconductor devices having copper interconnections, there may be provided about ten CMP apparatuses for a copper interconnection process and about five copper plating apparatuses per a plant. The total flow rate of waste water containing copper discharged from these apparatuses becomes as high as about 220 m³/day at the maximum, and the total amount of copper contained in the waste water becomes as much as about 22 kg-Cu/day at the maximum. Thus, there has been strongly required to efficiently recover and reuse copper from waste water in view of resource saving as well as environmental protection.

In a conventional installation industry including a semiconductor device fabrication industry, waste water has been treated by a comprehensive waste water treating system in which waste water has been collected from various processes in a plant and has been collectively treated. However, in a semiconductor device fabrication industry in which fabrication processes have been rapidly improved, there has been required to treat waste water discharged from respective processes on the point of use, i.e., at locations where-water has been used. This reason is as follows: Production systems have changed from conventional non-diversified and mass production into diversified and minor production. Types of products are changed so frequently that variation of properties of waste water becomes numerous. The conventional waste water treating system cannot sufficiently cope with the variation of properties of waste water. Additionally, a system in which waste water produced in respective processes is respectively treated can facilitate recovery and reuse of metal as compared to the conventional comprehensive waste water treating system.

Because a concentration of copper in waste water produced in chemical mechanical polishing (CMP) process or waste water produced in copper plating is normally 100 mg/l or lower, heretofore an electrolytic deposition process has not been used for recovering copper from the waste water due to the problem of operating voltage rise and efficiency. Further, copper is adsorbed and recovered by ion exchange resin as copper ions in an ion exchange resin process, and copper is precipitated and recovered in the form of hydroxide or oxide in a coagulating sedimentation process, and hence further treatment is required to recycle the recovered copper in both processes. Additionally, in the ion exchange resin process, frequency of replacement of the ion exchange resin is high, and is thus troublesome.

Solution containing metal ions as water to be treated is treated typically by the following methods: (1) a precipitation method in which chemicals are added to waste water so as to form insoluble hydroxide or sulfide, (2) an ion exchange method in which metal ions are absorbed by an ion exchange resin, and (3) an electrolytic deposition method in which metal is deposited on a surface of a cathode due to electrochemical reaction.

The precipitation method is problematic in that a large amount of chemicals is used and a secondary treatment is required to treat metal-containing sludge which is by-product. Particularly, when treating copper-containing waste water, the precipitated copper hydroxide has a high water content, i.e., is sludge having a small copper content per unit volume, and metal hydroxide which is difficult to be reused is produced in large quantities. Further, copper hydroxide, i.e., metal hydroxide, should be stored in such a manner that copper is not dissolved again and does not pollute the environment.

The ion exchange method can sufficiently absorb and remove metal ions, but is problematic in that a large amount of acid is required to regenerate the ion exchange resin which was saturated due to absorption and a secondary treatment is required to treat metal-containing concentrated waste water.

In the electrolytic deposition method, generally, waste water having a metal ion concentration of not less than 200 mg/l can be efficiently treated and high-purity metal can be recovered without by-product. However, in a case where the electrolytic deposition method is applied to treatment of waste water having a low metal ion concentration of not more than 100 mg/l, efficiency of removing the metal ions is low, and it is difficult to remove the metal ions stably down to very low concentration. Particularly, when treating copper-containing waste water, if copper concentration of the waste water is low, deposited copper is dissolved again, and hence it is difficult to make the copper concentration stably to not more than 3 mg/l, much less to not more than 0.5 mg/l.

Further, now that recognition and measures of environmental management have been rapidly widespread, enforcement of a law, introduction of the ISO standard, and the like have brought about the necessity of treatment of sludge or high-concentration waste water, which has been treated by industrial waste treatment contractors, by individual own companies.

Furthermore, in a case where the properties of waste water are changed in evolution of fabrication processes such as semiconductor device fabrication process, treatment conditions of waster water become different, and hence it is difficult to set treatment conditions of waste water in a method in which mixed waste water of various processes is treated by a large-scale comprehensive waste water treating system. Additionally, it is generally difficult to separate and recover metals as valuable materials.

From these points of view, there has been a demand for technology capable of highly separating and recovering metals from waste water without producing by-product at the place (POU: point of use) where waste water is produced, and reducing the metal ion concentration to the degree to which treated water can be discharged to the outside.

Particularly, in a case where waste water produced in a semiconductor device fabrication process such as a CMP process or a plating process for a copper interconnection process is treated, installation location is in a clean room and its neighborhood whose construction cost is high, and therefore a waste treatment facility having a small installation area is desirable.

The electrolytic deposition method is a method of recovering metals by depositing metal ions dissolved in waste water onto a cathode. This method is easy to operate at a low cost, and has been used as a copper recovery method in technical scale for more than 100 years. However, this method has the following problems in treating semiconductor fabrication process waste water, such as CMP waste water or water used in a plating apparatus, which has a low concentration and exhibits unstable properties.

The first problem is that, in order to carry out the electrolytic deposition in an industrial manner, metal should be stably and preferably continuously extracted from the electrolytic cell. If metal ions in waste water are copper ions, copper can be easily deposited by electrolysis in the form of powders or fine particles. Therefore, copper powders can be extracted from the electrolytic cell. However, in order to stably extract the copper powders, the deposition state of the copper powders should be kept constant, and scraping the copper powders off the cathode and extracting the copper powders from a cathode chamber should be carried out stably and continuously.

The second problem is that, in order to apply the electrolytic deposition to the waste water treatment, a concentration of metal ions contained in treated water, which is to be discharged through an outlet of the electrolytic cell, is required to stably decrease to a desired permissible concentration. If the concentration of metal ions contained in the treated water at the outlet of the electrolytic cell cannot stably decrease to the permissible concentration, the treated water should be returned to an inlet of the waste water treatment apparatus so that the concentration of the metal ions decreases to the permissible concentration. As a result, processes become complicated, the facility becomes large, and a treatment cost becomes high. Instead of returning the treated water to the inlet of the waste water treatment apparatus, an additional process such as an ion exchange resin process may be provided. However, in this case, the number of components of the facility increases, thus causing the facility to become large.

The electrolytic deposition method is a metal separation and recovery method which has been used for more than 100 years, and the electrolytic deposition apparatus which has been proposed heretofore includes a flat-plate electrolytic cell, a fluidized-bed electrolytic cell, a double cylindrical electrolytic cell, and a rotating electrolytic cell.

A flat-plate electrolytic cell is an electrolytic deposition cell having the simplest structure in which an anode plate and a cathode plate are disposed so as to face each other in a rectangular cell.

A fluidized-bed electrolytic cell is a system in which while minute conductive particles are fluidized and flow downwardly through a space between counter flat-plate electrodes or double cylindrical electrodes, metals are deposited on the particles, and are then taken out continuously. In the fluidized-bed electrolytic cell, since it is necessary to disperse particles sufficiently so that the particles between the electrodes do not adhere to each other, only an electrolytic cell having a small capacity can be manufactured, and in some cases, an industrial-scale electrolytic cell which can treat the quantity of waste water produced in a semiconductor device fabrication apparatus cannot be manufactured. Further, the particles fluidized between the electrodes become bipolar, and a phenomenon in which surfaces of the particles at the cathode side of the electrolytic cell become an anode and metals deposited on the surfaces of the particles are dissolved again occurs. In a case where copper-containing waste water is treated, in some cases, the concentration of metals contained in the treated water at the outlet of the electrolytic cell cannot be lowered stably to the permissible concentration or less, because copper has such properties as to be easily dissolved at the anode.

A double cylindrical electrolytic cell is a system in which metals are deposited in the form of powders on a surface of a cathode by flowing solution through a narrow gap between a cathode and an anode by the upflow which are vertically concentrically disposed, and then powdered metals are removed from the surface of the cathode and recovered by flowing backwashing water by the downflow while applying vibration to the cathode as needed. However, because the state of the cathode surface varies with time, it is difficult to stably obtain powdered deposited materials, which can be easily removed. Immediately after backwashing which is required to be performed frequently, in some cases, the quality of treated water cannot be stable.

The rotating electrolytic cell is a system in which an anode is disposed outside a hanging-bell shaped cathode, and metals are deposited on a surface of the cathode while rotating the cathode. Although the rotating electrolytic cell has a more complicated structure than the flat-plate electrolytic cell, the thickness of diffusion layer on the surface of the cathode can be thin by rotating the cathode at a high speed, and thus the metal concentration in the treated water can be lowered.

In the rotating electrolytic cell, a scraper is disposed in the vicinity of the surface of the rotating cathode to recover grown deposited metals, and thus continuous operation can be performed without removing the cathode outwardly of the cell. Generally, in a case where the deposited metals adhere to the cathode to which current is supplied, the deposited metals are not dissolved again. However, when the deposited metals are removed from the cathode, the metals are partly dissolved again, and deposition of metals progresses. Thus, when the concentration of solution becomes low, deposition and dissolution become in equilibrium state, and in some cases, the metal ion concentration in the treated water cannot be sufficiently lowered.

DISCLOSURE OF INVENTION

It is an object of the present invention to provide an electrolytic deposition treatment apparatus and method which can reduce metal ion concentration of waste water to be treated by electrolytic deposition to the degree to which treated water can be discharged to the outside, and which can treat waste water, even if the quantity of waste water produced in a semiconductor device fabrication apparatus is large.

For the purpose of solving the above drawbacks, the inventors of the present invention have found from an extensive study that metal ions in waste water are deposited on a surface of a rotating cathode as metals, a cation exchange membrane is disposed around the cathode through a water layer interposed therebetween, and a gas permeable anode is disposed on an outer circumferential surface of the cation exchange membrane through a cation exchanger interposed therebetween, whereby removed metals are not dissolved again and the above drawbacks can be solved. More specifically, in a rotating electrolytic cell in which a cathode chamber and an anode chamber are partitioned so that oxygen gas generated in the anode chamber is prevented from flowing into the cathode chamber, metals deposited on the surface of the cathode are scraped off by a scraper, the scraped metals are continuously captured through a pumped flow by a bag filter disposed outside the rotating electrolytic cell, and thus the removed metals are prevented from being dissolved again. Thus, the above drawbacks can be solved.

In order to achieve the above objects, according to an aspect of the present invention, there is provided an electrolytic deposition treatment apparatus comprising: a cathode for depositing metal ions in water to be treated as metal; a cation exchange membrane disposed so as to face the cathode; and an anode disposed so as to face the cation exchange membrane through a cation exchanger; wherein the water to be treated is supplied to a space between the cathode and the cation exchange membrane.

Further, pure water is supplied to an anode chamber having the anode therein.

Further, the anode chamber having the anode therein and an cathode chamber having the cathode therein are partitioned to prevent oxygen gas generated in the anode chamber from flowing into the cathode chamber.

Further, the anode chamber having the anode therein and an cathode chamber having the cathode therein are partitioned. An inert gas is introduced into the cathode chamber to make the cathode chamber positive pressure, the inert gas flows through a gap between the anode chamber and the cathode chamber into the anode chamber, and oxygen gas generated in the anode chamber is discharged together with the inert gas from the anode chamber.

Further, the cathode is rotatable.

Further, a scraper is disposed in contact with or adjacent to the rotatable cathode so that the scraper scrapes off the metal deposited on the cathode.

Further, the metal removed from the surface of the cathode by the scraper is delivered to a filter together with treated water, and is filtrated and captured by the filter.

Further, filtrate which has passed through the filter is introduced in the tangential direction of the cathode into the cathode chamber.

Further, the anode comprises a gas-permeable anode.

Further, the cation exchanger is made of ion-exchange fibrous materials.

Further, the ion-exchange fibrous materials comprise materials in which ion exchange group is introduced into organic polymer unwoven fabric substrates by utilizing radiation-induced graft polymerization.

According to an aspect of the present invention, there is provided an electrolytic deposition method comprising: supplying water to be treated having a pH of a predetermined range between a cathode and a cation exchange membrane; depositing metal on the cathode by applying direct voltage between an anode and the cathode, the anode being disposed in an anode chamber to which pure water is supplied; and removing the deposited metal on the cathode.

Further, the cathode is rotated.

Further, the metal deposited on the surface of the cathode is scraped off by a scraper disposed in contact with or adjacent to the rotatable cathode.

Further, the metal removed from the surface of the cathode is filtrated and captured by a filter.

Further, the pH is in the range of 1 to 3.

Further, the anode comprises a gas-permeable anode.

Further, the water to be treated is waste water produced in a semiconductor device fabrication apparatus or waste water pretreated after being produced in the semiconductor device fabrication apparatus.

Further, metal ions in the water to be treated are copper ions produced in a semiconductor device fabrication apparatus for use in a copper interconnect forming process.

According to the present invention, metal ion concentration in waste water can be reduced by electrolytic deposition to the degree to which treated water can be discharged to the outside, and waste water can be treated, even if the quantity of waste water produced in a semiconductor device fabrication apparatus is large. Additionally, since the cathode is a rotating type and deposited metals can be continuously scraped off, frequent replacement of the cathode is not required even in large quantity of the deposited metals. For scraping the deposited metals off, for example, a scraper disposed in the vicinity of the cathode can be used.

Further, since a water bath having an anode therein and a water bath having an cathode therein are partitioned by a cation exchange membrane, oxygen generated in the anode can be prevented from being dissolved in the water bath having the cathode therein, re-dissolution of the deposited metals caused by oxidization can be suppressed, and the metal ion concentration in treated water can be lowered to a very small quantity.

Furthermore, pure water can be used as electrode water which is supplied to the water bath having the anode therein, and even if liquid to be treated has strong corrosiveness as liquid to be treated having strong acidity, deterioration of the anode can be suppressed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view showing an electrolytic deposition treatment apparatus according to an embodiment of the present invention;

FIG. 2 is a schematic view showing an example in which raw water is introduced in a tangential direction of a cylindrical electrolytic cell so that the raw water revolves;

FIG. 3 is a schematic view showing an electrolytic deposition treatment apparatus according to another embodiment of the present invention;

FIG. 4 is a schematic view showing an electrolytic deposition treatment apparatus according to still another embodiment of the present invention;

FIG. 5 is a schematic view showing an electrolytic deposition treatment apparatus according to still another embodiment of the present invention; and

FIGS. 6A through 6E show an example of a process of forming interconnections.

BEST MODE FOR CARRYING OUT THE INVENTION

Various embodiments of the present invention will now be described with reference to the drawings. In the drawings, like or corresponding parts are denoted by the same numerals.

FIG. 1 is a schematic view showing an electrolytic deposition treatment apparatus according to an embodiment of the present invention.

As shown in FIG. 1, the electrolytic deposition treatment apparatus 1 comprises an electrolytic cell 2, a substantially cylindrical cathode 3 disposed in the electrolytic cell 2, a cation exchange membrane 4 disposed in the electrolytic cell 2 and located outside the cathode 3, and an anode 6 surrounding an outer circumferential surface of the cation exchange membrane 4 through a cation exchanger 5 interposed therebetween.

A rotational shaft 7 is provided on the cathode 3 so that the cathode 3 is rotated by a motor (not shown) coupled to the rotational shaft 7. The anode 6 is made of gas-permeable material. A direct-current power source (not shown) is provided to allow direct current to flow between the cathode 3 and the anode 6. A scraper 8 is disposed adjacent to the cathode 3 for scraping off a part of metal deposited on the surface of the cathode 3. The inside of the electrolytic cell 2 is divided by the cation exchange membrane 4 into an anode chamber 9 and a cathode chamber 10. A circulation line 11 extends from the bottom of the electrolytic cell 2. A circulation pump 12 and a bag filter 13 are provided on the circulation line 11.

In the electrolytic deposition treatment apparatus 1 shown in FIG. 1, raw water (waste water to be treated) is firstly introduced into the cathode chamber 10 formed between the rotating cathode 3 and the cation exchange membrane 4. The direct current is applied between the cathode 3 and the anode 6, so that metal ions in the waste water are deposited on the surface of the cathode 3 in the form of powder metal or acicula metal. A part of the deposited metal is removed from the surface of the cathode 3 by the scraper 8 disposed adjacent to the surface of the cathode 3. The metal removed from the surface of the cathode is led into the circulation line 11 provided on the bottom of the electrolytic cell 2, and is then recovered by the bag filter 3. Since the surface of the cathode 3 is scraped by the scraper 8 at all times, the condition of the surface of the cathode 3 is kept constant. Accordingly, a state of the metal deposited on the cathode 3 can be easily controlled by adjusting an electrolyte solution, a current density, a rotational speed of the cathode 3, and the like.

The cation exchanger 5 is disposed between the gas-permeable anode 16 and the cation exchange membrane 4, and pure water is supplied to the anode chamber 9 in which the anode 6 is disposed. With this structure, although an oxygen gas is produced due to pure water electrolysis occurring on the surface of the anode 6 which is in contact with the cation exchanger 5, the oxygen gas does not enter the cathode chamber 10 because the oxygen gas is intercepted by the cation exchange membrane 4. Accordingly, the metal removed from the cathode 3 is not dissolved again and is not formed into the metal ions. Additionally, since the waste water does not come into direct contact with the anode 6, even if the waste water is highly corrosive, the anode 6 does not deteriorate. After the metal ions are recovered as metal, the water is extracted from the cathode chamber 10 disposed between the cathode 3 and the cation exchange membrane 4.

Instead of providing the above-mentioned structure in which the anode chamber 9 and the cathode chamber 10 are isolated from each other as shown in FIG. 1, the anode chamber 9 and the cathode chamber 10 may communicate with each other as shown in FIG. 5. In this structure, a pressurized inert gas containing no oxygen is supplied to the cathode chamber 10 so as to form a gas flow running from the cathode chamber to the anode chamber. Such a gas flow prevents oxygen, which is produced in the anode chamber, from entering the cathode chamber, and can therefore prevent the removed metal from being dissolved again. Nitrogen gas or argon gas is suitably used as the inert gas to be supplied.

In the electrolytic deposition treatment apparatus 1 shown in FIG. 1, the anode 6 and the cation exchanger 5 are in contact with each other in the anode chamber 9 in the presence of pure water. Therefore, under electric potential gradient, pure water electrolysis easily occurs on the anode surface which is in contact with the cation exchanger 5, thereby producing an oxygen gas and H+ ions. The oxygen gas passes through the anode 6, which is a gas-permeable electrode, to enter the anode chamber 9 behind the anode 6, and is then discharged to the exterior of the unit. The H+ ions migrate through the cation exchanger 5 and the cation exchange membrane 4 into the cathode chamber 10 due to electric potential gradient. Since the pure water is consumed in electrolysis, replenishment of pure water is required. Pure water may be supplied in such an amount that excessive pure water overflows from the anode chamber 9, or pure water may be circulated and supplied.

The metal is reduced to be deposited on the surface of the cathode 3. As the concentration of the metal ions becomes low, the H+ ions are also reduced to a hydrogen gas. The hydrogen gas produced on the surface of the cathode 3 is discharged out of the system. The hydrogen gas may be discharged together with a diluent gas which is introduced to the system from outside, or may be introduced into the anode chamber 9 and then extracted from the anode chamber 9 together with the oxygen gas produced on the surface of the anode 6. The diluent gas is preferably such that oxygen is not dissolved in the cathode liquid. Nitrogen gas or inert argon gas is preferably used as the diluent gas. The cathode 3 may have a smooth surface for the purpose of improving the capability of removal of the deposited metal. Further, the cathode 3 may have a large surface area for the purpose of decreasing current density so that the metal can be deposited in the form of acicula or powder. For example, the surface of the cathode 3 may have concave portions and convex portions. In this manner, various types of surfaces can be applied.

In view of efficiency and uniformity of deposition of the metal on the surface of the cathode 3, it is preferable to sufficiently agitate treated water in the electrolytic cell 2. The agitation of the waste water (raw water) can be made, for example, by increasing the rotational speed of the cathode or by introducing the waste water in a tangential direction of the cathode 3 so that the waste water revolves.

FIG. 2 is a schematic view showing an example in which the raw water is introduced in the tangential direction of the cylindrical electrolytic cell 2 and the cylindrical cation exchange membrane 4 so that the raw water revolves.

A space between the cation exchange membrane 4 as an ion exchange membrane and the anode 6 is filled with the cation exchanger 5 as an ion exchanger. As the ion exchanger, it is possible to use a known ion exchange resin or an ion exchange resin formed by a binder. It is also possible to use an ion exchange resin bonded to a porous base, e.g., sponge, or a textile base. However, as the ion exchanger, it is preferable to use a fibrous material comprising polymer fibrous substrates to which ion-exchange groups are introduced by graft polymerization. The substrates of polymer fibers to be grafted may either be single fibers of a polyolefin such as polyethylene or polypropylene, or composite fibers comprising a core portion and a sheath portion in which the core portion and the sheath portion are made of different polymers respectively. The ion exchanger, which is obtained by introducing ion-exchange groups into the composite fibers by a radiation-induced graft polymerization, is excellent in the ion-exchange capacity and is distributed continuously, and is therefore desirable to be used. The ion-exchange fibrous material may be in the form of a woven fabric, nonwoven fabric, or the like.

The radiation-induced graft polymerization is a technique for introducing a monomer into polymer substrates by irradiating the polymer with radiation rays so as to produce a radical which reacts with the monomer.

Radiation rays usable for the radiation-induced graft polymerization include α-rays, β-rays, γ-rays, electron beam, ultraviolet rays, and the like. Of these, γ-rays or electron beam may preferably be used in the present invention. As the radiation-induced graft polymerization method, there are a pre-irradiation graft polymerization comprising previously irradiating graft substrates with radiation rays and then contacting the substrates with a grafting monomer, and a co-irradiation graft polymerization method in which irradiation of radiation rays is carried out in the co-presence of substrates and a grafting monomer. Both of these methods may be employed in the present invention. Further, depending upon the manner of contact between a monomer and substrates, there are polymerization methods such as a liquid-phase graft polymerization method in which polymerization is effected while substrates are immersed in a monomer solution, a gas-phase graft polymerization method in which polymerization is effected while substrates are in contact with vapor of monomer, and an immersion gas-phase graft polymerization method in which substrates are firstly immersed in a monomer solution and then taken out of the monomer solution and a polymerization is effected in a gas phase. Either method of polymerization may be employed in the present invention.

The ion-exchange groups to be introduced into fibrous substrates such as a nonwoven fabric are not particularly limited. Various kinds of cation-exchange groups can be used. For instance, usable cation-exchange groups include strongly acidic cation-exchange groups such as sulfo group, moderately acidic cation-exchange groups such as phosphoric group, and weakly acidic cation-exchange groups such as carboxy group.

These various ion-exchange groups can be introduced into fibrous substrates by subjecting a monomer having such an ion-exchange group to graft polymerization, preferably radiation-induced graft polymerization, or by subjecting a polymerizable monomer having a group that is changeable into an ion-exchange group, to graft polymerization, followed by conversion of that group into the ion-exchange group. Monomers having an ion-exchange group usable for this purpose may include acrylic acid (AAc), methacrylic acid, sodium styrenesulfonate (SSS), sodiummethallylsulfonate, sodium allylsulfonate, sodium vinylsulfonate, vinylbenzyl trimethylammonium chloride (VBTAC), diethylaminoethyl methacrylate, and dimethylaminopropylacrylamide. Sulfo group as a strongly acidic cation-exchange group, for example, may be introduced directly into substrates by carrying out radiation-induced graft polymerization in which sodium styrenesulfonate is used as a monomer. The monomer having groups that can be converted into ion-exchange groups may include acrylonitrile, acrolein, vinylpyridine, styrene, chloromethylstyrene, and glycidyl methacrylate (GMA). Sulfo group as a strongly acidic cation-exchange group, for example, may be introduced into substrates in such a manner that glycidyl methacrylate is introduced into the substrates by radiation-induced graft polymerization, and then react with a sulfonating agent such as sodium sulfite.

FIG. 3 is a schematic view showing an electrolytic deposition treatment apparatus according to another embodiment of the present invention. In the embodiment shown in FIG. 1, the treated water is extracted from the cathode chamber 10. In this embodiment shown in FIG. 3, the treated water is extracted after passing through the bag filter 13. Other structures of this embodiment shown in FIG. 3 are the same as those of the embodiment shown in FIG. 1.

FIG. 4 is a schematic view showing an electrolytic deposition treatment apparatus according to still another embodiment of the present invention. In the embodiment shown in FIG. 4, a storage vessel 14 is disposed to store treated water and the treated water extracted from the cathode chamber 10 is stored in the storage vessel 14. The treated water stored in the storage vessel 14 can be returned by a pump 15 to the cathode chamber 10 disposed between the cathode 3 and the cation exchange membrane 4. Other structures of this embodiment are the same as those of the embodiment shown in FIG. 1.

Next, a specific example of the electrolytic deposition treatment apparatus 1 shown in FIG. 1 will be described.

The anode 6 is formed from a plate-like lath metal which is made of Ti plated with Pt. The cathode 3 is made of SUS 304 and has a smooth surface. The rotational speed of the cathode 3 is in the range of 1 to 500 rpm (min⁻¹). Current density on the surface of the cathode 3 is in the range of 1 to 10 A/dm². The inner surface and a water-surface portion of the outer surface of the cathode 3 are coated with Teflon (registered trademark) resin so that the metal can be deposited only on a predetermined portion of the outer surface. Although the cathode liquid (raw water) containing metal ions can be supplied in a batch manner, it is preferable that the cathode liquid is continuously supplied to and extracted from the cathode chamber 10. This is because supplying the cathode liquid in this manner can suppress the fluctuation of the concentration of the metal ions in the cathode chamber 10, and is therefore preferable in view of electrolytic deposition conditions. FIG. 1 also shows one example of the manner of supplying the cathode liquid. Specifically, the cathode liquid (raw water) is supplied to the outer side of the rotating cathode 3 from above so that the cathode liquid overflows from a top portion of a weir provided inside the rotating cathode 3. Supplying the cathode liquid in this manner is preferable because the metal powders scraped off by the scraper 8 do not flow out of the cathode chamber 10. It is further preferable to supply the cathode liquid from the side surface of the cathode chamber 10 in the tangential direction of the cathode 3 so as to form a counterflow against the rotational direction of the rotating cathode 3 because a thickness of a diffusion layer on the surface of the cathode 3 can be reduced.

The metal powders, which were scraped off by the scraper 8, are circulated by a pump flow through an outlet nozzle disposed on the bottom of the cathode chamber 10, and are filtrated by the bag filter 13. Hole diameter of the bag filter 13 is in the range of 1 to 10 μm.

The anode 6 is preferably made of materials used for an insoluble electrode. For example, Ti plated with Pt is used to form the anode 6. The anode 6 preferably has a porous structure such as mesh or lath mesh (expanded metal). The cathode 3 is preferably made of stainless steel. The rotational speed of the cathode 3 is in the range of 1 to 500 rpm (min⁻¹), preferably in the range of 50 to 200 rpm (min⁻¹). A distance between the cathode 3 and the anode 6 can be selected within a range of 20 to 50 mm. Current density on the surface of the cathode is preferably in the range of 2 to 3 A/dm². Hole diameter of the bag filter 13 is preferably in the range of 1 to 10 μm. An outlet port of the treated water may be provided on the cathode chamber or the outlet of the bag filter. The scraper 8 is preferably made of resin or ceramic having an excellent chemical resistance. A distance between the scraper 8 and the cathode 3 is preferably in the range of 0.5 to 5 mm.

It is preferable that raw water (i.e., water to be treated) to be supplied to the apparatus is pretreated. Specifically, substances which have negative influence on electrolytic deposition are preferably removed or separated from the raw water, and the raw water is preferably concentrated in order to improve the efficiency of electrolytic deposition, as needed. Using an activated carbon and an ion exchange resin, an oxidizing agent such as hydrogen peroxide contained in the waste water is decomposed by the activated carbon, and then the ion exchange resin is used to absorb metal ions so as to remove them from the waste water. The ion exchange resin can be regenerated by acid. According to this pretreatment process, an acid solution of 0.5 to 5 g/l (liter), which is suitable for electrolytic deposition, can be obtained. Additionally, as shown in an earlier Japanese patent application No. 2003-125889 (not published) filed by the applicants of the present invention, the raw water may be pretreated by a combination of a platinum-supported catalyst and electrodialysis. This pretreatment process is more preferable because an acid solution of about 0.5 to 1 g/l, which is suitable for electrolytic deposition, can be continuously obtained. Depending on the properties of the raw water, the pretreatment may not be required. In such a case, the waste water can be directly introduced into the electrolytic deposition process.

The present invention will be further described below with reference to specific examples. It should be noted that one of the specific examples of the present invention will be described by the following examples, and the present invention is not limited to the following examples.

EXAMPLE 1

Waste water having Cu concentration of 500 mg/l and a pH of 1 was treated using the electrolytic deposition treatment apparatus shown in FIG. 1, and the waste water passed through the electrolytic deposition treatment apparatus at a flow rate of 0.6 m³/hr for 24 hours.

The operational conditions were set as follows: cathode area 20 dm², anode-cathode distance 30 mm, volume of electrolytic cell 101 (liter), rotational speed of cathode 100 rpm(m⁻¹), current density 3 A/dm², circulating flow rate to bag filter 1 m³/hr, hole diameter of bag filter 5 μm.

In this case, voltage was not greater than 10V. As a result, it was confirmed that the throughput of powdery copper metals was 1.3 kg/day without replacement of the cathode. Dissolution of recovered copper metal caused by oxidization was not observed. Further, deterioration of the anode was not observed at all.

EXAMPLE 2

Waste water was treated using the electrolytic deposition treatment apparatus with the same raw water and under the same operational conditions as in the Example 1. The apparatus shown in FIG. 3 is different from the apparatus shown in FIG. 1 in that the outlet of the treated water corresponds to the outlet of the bag filter in the apparatus shown in FIG. 3. As a result, it was confirmed that the throughput was 1.3 kg/day also in the structure shown in FIG. 3.

EXAMPLE 3

The electrolytic deposition treatment apparatus shown in FIG. 4 was filled with 100 l of waste water having Cu concentration of 500 mg/l and a pH of 1, and the waste water passed through the electrolytic deposition treatment apparatus at a flow rate of 0.6 m³/hr for 24 hours.

The operational conditions were set as follows: cathode area 20 dm², anode-cathode distance 30 mm, volume of cathode chamber 101, rotational speed of cathode 100 rpm(m⁻¹), current density 0.5 A/dm², circulating flow rate to bag filter 1 m³/hr, hole diameter of bag filter 5 μm.

In this case, voltage was not greater than 10V. As a result, the copper concentration of the waste water was lowered to less than 0.5 mg/l by operating the electrolytic deposition treatment apparatus for 16 hours. Thus, it was verified that the copper concentration was lowered to a low concentration of 0.5 mg/l by the present apparatus.

EXAMPLE 4

The electrolytic deposition treatment apparatus shown in FIG. 4 was filled with 100 l of waste water having Cu concentration of 500 mg/l and a pH of 1, and the waste water passed through the electrolytic deposition treatment apparatus at a flow rate of 0.6 m³/hr for 24 hours.

The operational conditions were set as follows: cathode area 20 dm², anode-cathode distance 30 mm, volume of electrolytic cell 101, rotational speed of cathode 100 rpm(m⁻¹), circulating flow rate to bag filter 1 m³/hr, hole diameter of bag filter 5 μm.

The current density was 4.0 A/dm² until operating time of three hours, and 0.5 A/dm² after operating time of three hours. As a result, the copper concentration of less than 0.5 mg/l was obtained after operating time of 8 hours. In this case, voltage was not greater than 10V. Thus, it was verified that the copper concentration was lowered to a low concentration of 0.5 mg/l by the present apparatus.

INDUSTRIAL APPLICABILITY

The present invention is suitable for use in an electrolytic deposition treatment apparatus and method for removing metals efficiently and highly from various kinds of liquids and recovering the metals continuously in the form of granules or powder. 

1. An electrolytic deposition treatment apparatus comprising: a cathode for depositing metal ions in water to be treated as metal; a cation exchange membrane disposed so as to face said cathode; and an anode disposed so as to face said cation exchange membrane through a cation exchanger; wherein the water to be treated is supplied to a space between said cathode and said cation exchange membrane.
 2. The electrolytic deposition treatment apparatus as recited in claim 1, wherein pure water is supplied to an anode chamber having said anode therein.
 3. The electrolytic deposition treatment apparatus as recited in claim 1, wherein said anode chamber having said anode therein and an cathode chamber having said cathode therein are partitioned to prevent oxygen gas generated in said anode chamber from flowing into said cathode chamber.
 4. The electrolytic deposition treatment apparatus as recited in claim 1, wherein said anode chamber having said anode therein and an cathode chamber having said cathode therein are partitioned; and wherein an inert gas is introduced into said cathode chamber to make said cathode chamber positive pressure, said inert gas flows through a gap between said anode chamber and said cathode chamber into said anode chamber, and oxygen gas generated in said anode chamber is discharged together with said inert gas from said anode chamber.
 5. The electrolytic deposition treatment apparatus as recited in claim 1, wherein said cathode is rotatable.
 6. The electrolytic deposition treatment apparatus as recited in claim 5, further comprising a scraper disposed in contact with or adjacent to said rotatable cathode so that said scraper scrapes off the metal deposited on said cathode.
 7. The electrolytic deposition treatment apparatus as recited in claim 6, wherein the metal removed from the surface of said cathode by said scraper is delivered to a filter together with treated water, and is filtrated and captured by said filter.
 8. The electrolytic deposition treatment apparatus as recited in claim 7, wherein filtrate which has passed through said filter is introduced in the tangential direction of said cathode into said cathode chamber.
 9. The electrolytic deposition treatment apparatus as recited in claim 1, wherein said anode comprises a gas-permeable anode.
 10. The electrolytic deposition treatment apparatus as recited in claim 1, wherein said cation exchanger is made of ion-exchange fibrous materials.
 11. The electrolytic deposition treatment apparatus as recited in claim 10, wherein said ion-exchange fibrous materials comprise materials in which ion exchange group is introduced into organic polymer unwoven fabric substrates by utilizing radiation-induced graft polymerization.
 12. An electrolytic deposition treatment method comprising: supplying water to be treated having a pH of a predetermined range between a cathode and a cation exchange membrane; depositing metal on said cathode by applying direct voltage between an anode and said cathode, said anode being disposed in an anode chamber to which pure water is supplied; and removing the deposited metal on said cathode.
 13. The electrolytic deposition treatment method as recited in claim 12, wherein said cathode is rotated.
 14. The electrolytic deposition treatment method as recited in claim 13, wherein the metal deposited on the surface of said cathode is scraped off by a scraper disposed in contact with or adjacent to said rotatable cathode.
 15. The electrolytic deposition treatment method as recited in claim 14, wherein the metal removed from the surface of said cathode is filtrated and captured by a filter.
 16. The electrolytic deposition treatment method as recited in claim 12, wherein said pH is in the range of 1 to
 3. 17. The electrolytic deposition treatment method as recited in claim 12, wherein said anode comprises a gas-permeable anode.
 18. The electrolytic deposition treatment method as recited in claim 12, wherein the water to be treated is waste water produced in a semiconductor device fabrication apparatus or waste water pretreated after being produced in said semiconductor device fabrication apparatus.
 19. The electrolytic deposition treatment method as recited in claim 12, wherein metal ions in the water to be treated are copper ions produced in a semiconductor device fabrication apparatus for use in a copper interconnect forming process. 